The neural crest is a transient structure that forms early in vertebrate development. Cells derived from the crest migrate to many different sites in the embryo where they give rise to a diverse array of cell types, such as melanocytes, glia and many different types of neurons of the autonomic nervous system, including the enteric nervous system of the gut. Some of the lineage decisions made by neural crest-derived cells are influenced by the microenvironments through which they migrate and in their final sites of arrest. Growth factors, implicated to play important roles in the decisions made by crest-derived cells, are frequently present in the cellular microenvironments. The experiments in this proposal will test the hypothesis that basic fibroblast growth factor in the proposal will test the hypothesis that basic fibroblast growth factor in the posterior branchial arches of early avian embryos influences the choice of the melanocytic phenotype by crest-derived cells. The presence of three related molecules, basic fibroblast growth factor, its cell surface receptor, and the messenger RNA for the receptor will be determined in the posterior branchial arches of normal chick and quail embryos and in mutant Silkie embryos that develop abnormal pigmentation of the viscera. Two questions will be asked: 1) what is the time course of expression of each of the three molecules? 2) what is the spatial distribution of the cells expressing the molecules? Techniques to be used include immunohistochemistry an in situ hybridization. These studies will provide insights into the normal progression of events that occur when cells follow the pathway leading to melanogenesis. Understanding the cues that regulate the expression of the melanocytic phenotype by neural crest-derived cells will lead to a better comprehension of the underlying causes of malignant, a cancer that is one of the most rapidly increasing in incidence. Results of these investigations will affect the practice of nurse clinicians and researchers, particularly those in oncology. If these three related molecules have a function in the commitment of melanocytes, a new parameter might be used for identifying persons at risk for developing malignant malanoma. Nurse researchers could devise clinical studies using information about these molecules to detect skin changes, leading to earlier detection and treatment. It would also affect education and counseling of the public.